656 



ELECTROTONIC CURRENTS IN NERVES AND IN MUSCLES. 



presence of abundant watery secretion, the first phase preponderates, while when 

 the secretion is less abundant and more viscid the second phase preponderates. 



CURRENTS IN NERVES AND IN MUSCLES IN THE 

 ELECTROTONIC STATE. 



If a nerve be connected with non-polarizable electrodes in such a manner that 

 its transverse section is applied to the one and its surface to the other (Fig. 231, 

 I), the multiplicator will indicate the presence of a strong nerve-current. If a 

 constant electrical current, designated the polarizing current, be now passed 

 through the length of the extremity of the nerve projecting beyond the electrode, 

 in a direction which coincides with that of the current in the nerve, the 

 magnetic needle exhibits a still more marked deflection, as a sign of increase in 

 the nerve-current positive phase of electrotonus. This is directly proportional 



to the length of nerve traversed and the strength 

 of the galvanic current, and inversely to the dis- 

 tance between the portion traversed and the por- 

 tions of the nerve applied to the pads. 



If, with the nerve in the same position, the 

 constant electrical current is passed in a direction 

 opposite to that of the nerve-current (II) , there is 

 a diminution in the electromotive force of the 

 latter negative phase of electrotonus. 



If the electrodes are applied to two points on 

 the surface of the nerve almost equidistant from 

 the equator (1 1 1), the galvanometer at first ex- 

 hibits no deflection with this ineffective arrange- 

 ment. If, now, a constant current be passed 

 through the free, projecting extremity of the 

 nerve, the magnetic needle exhibits electro- 

 motive activity in the same direction as the 

 constant current. 



ffl 



FIG. 231. 



The foregoing experiments demonstrate 

 that a nerve traversed by a constant elec- 

 trical current undergoes, not alone within 

 the directly traversed portion, but also 

 beyond this, an alteration in its electro- 

 motive activity that is designated electro- 

 tonus. This alteration is attended with a change in the irritability of 

 the nerve-segment in question. 



The electrotonic current is strongest near the electrodes. It may be 25 times 

 stronger than the resting nerve-current. Its strength increases with the strength 

 of the constant, polarizing current, likewise with the length of the segment tra- 

 versed. It is larger upon the side of the anode than upon that of the kathode. 

 It appears with the closing of the constant current, while it reaches its maximum 

 earlier at the kathode. It gradually increases at the anode and decreases at 

 the kathode. On tetanization it undergoes negative variation like the resting 

 nerve-current, while the polarizing current appears to be stronger. On the other 

 hand, no noteworthy electrotonic increase in current between the electrodes can 

 be observed beyond the polarizing current itself. Cold has a marked inhibiting 

 influence upon the production of the electrotonic current. 



The phenomena described occur only so long as the nerve is irritable. Ligation 

 of the extremity of the nerve projecting beyond the galvanometer-circuit abolishes 

 the phenomena in the segment so shut off. The galvanic electrotonic alterations 

 in the extrapolar segments described and due to a peculiar diffusion by physical 

 means of the polarizing current are wanting in the case of non-medullated nerves, 

 which on the other hand exhibit physiological electrotonus. By treating 

 medullated nerves with ether the physiological electrotonus may be abolished, 

 while the physical phenomena referred to persist. 



The negative variation appears more rapidly than the electrotonic increase 



